1. Field of the Invention
The present invention relates to a technology for detecting a liquid discharge failure in an inkjet recording apparatus.
2. Description of the Related Art
A typical image forming apparatus includes a plurality of nozzles that discharge droplets under a predetermined condition, a discharge-detecting unit that checks discharge of the droplets from the nozzles, and a recovery-control unit that controls timing of performing a recovery process on the nozzles based on the result of a check performed by the discharge-detecting unit. Such an image forming apparatus has been disclosed in Japanese Patent Application Laid-open No. 2005-280248. Strict regulations are imposed to improve the accuracy of detection of the droplets. For example, a diameter of a detection nozzle is made smaller than that of a recording nozzle, amplitude of a drive waveform of voltage for driving the detection nozzle is made smaller than that for driving the recording nozzle, and a rise time of the drive waveform for the detection nozzle is made longer than that for the recording nozzle.
On the other hand, in the method of monitoring droplets disclosed in Japanese Patent Application Laid-open No. 2005-083769, at least one pair of parallel laser lights is emitted, a nozzle discharges a droplet aiming between the laser lights, and each of light-receiving elements receives a corresponding laser light to perform photoelectric conversion. Because output signals from the light-receiving element momentarily drop when the droplet crosses the laser light, information on the droplet is obtained by detecting the output signals. For example, there is an image forming apparatus in which two pairs of parallel laser lights emitted at right angles, and its nozzle discharges a droplet aiming at an intersectional square.
However, the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 2005-280248 needs to include the detection nozzle in addition to the recording nozzle, and therefore its configuration is complicated. Furthermore, because the discharge of the droplets is checked using the detection nozzle instead of the recording nozzle that is actually used to record an image, the detection result is not completely reliable. On the other hand, the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 2005-083769 needs to include four light-emitting elements and four light-receiving elements to emit two pairs of parallel laser lights, resulting in high cost.